| 摘要 |
PURPOSE:To control and monitor gain and noise characteristics of an optical amplifier without the loss of an input signal and an output signal, by observing the power of spontaneous emission light which is amplified while travelling in the direction opposite to a signal light. CONSTITUTION:A light signal inputted in an optical input terminal 1 is mixed with a pumping light by a pumping light/signal light combiner 3, and enters a rare earth element added fiber 5 via an isolator 13. The above light signal travels while being amplified in the fiber 5, passes a post-stage optical isolator 4 for preventing oscillation and an optical bandpass filter, and is outputted from an optical output terminal 9. A pumping light source 8 is driven by a pumping light source driver 10 controlled by a control circuit 11. Spontaneous emission optical noise which is amplified while travelling in the direction opposite to signal amplification is taken out by an optical circulator 13. The taken- out light is converted to an electric signal by a photodiode 7 and monitored. On the basis of the monitored results, the pumping power is so controlled that, e.g. the monitored spontaneous emission noise becomes constant, thereby enabling operation of constant gain. |
